A battery-driven, low-field NMR unit for thermally and hyperpolarized samples

Abstract

The design of a multinuclear low-field NMR unit with variable field strength <6mT providing accurate spin manipulations and sufficient sensitivity for direct detection of samples in thermal equilibrium to aid parahydrogen-based hyperpolarization experiments. An optimized, resistive magnet connected to a battery or wall-power driven current source was constructed to provide a magnetic field <6mT. A digital device connected to a saddle-shaped transmit- and solenoid receive-coil enabled MR signal excitation and detection with up to 10(6) samples/s, controlled by a flexible pulse-programming software. The magnetization of thermally polarized samples at 1.8 and 5.7mT is detected in a single acquisition with a SNR≈10(1) and ≈10(2) and a line width of 42 and 32Hz, respectively. Nuclear spins are manipulated to an uncertainty of ±1° by means of pulses, which can be arranged in an arbitrary combination. As a demonstration, standard experiments for the measurement of relaxation parameters of thermally polarized samples were implemented. The detection of much stronger hyperpolarized signal was exemplified employing parahydrogen. Direct detection of thermal and hyperpolarized (1)H-MR signal in a single acquisition and accurate spin manipulations at 1.8and 5.5mT were successfully demonstrated.